Apparatus for electrochemical shaping



1966 K. F. TRAGER ET AL 3,

APPARATUS FOR ELECTROCHEMICAL SHAPING Filed Feb. 12, 1964 4 Sheets-Sheet 1 IN VENTORS Ke/w P55 5 21 A 652:3

E' BY JICKA. C2055 Nov. 29, 1966 K. F. TRAGER ETAL 3,283,699

APPARATUS FOR ELECTROCHEMICAL SHAPING 4 Sheets-Sheet 2 Filed Feb. 12, 1964 INVENTORS Kan/15.5 ZZ A 65/2 & B \[4CK A. (055 A TTOR/VE Y5 Nov. 29, 1966 TR ETAL 3,288,699

APPARATUS FOR ELECTROCHEMICAL SHAPING Filed Feb. 12, 1964 4 Sheets-Sheet Z INVENTORS Kim/ 55 E 7X 4 6.5264 BY JICK A. CROSS .4 TTO/P/VEYS Nov. 29, 1966 K. F. TRAGER ETAL 3,283,699

APPARATUS FOR ELECTROCHEMICAL SHAPING Filed Feb. 12, 1964 ca wa mas e 2% m W 6 7 1 40 4 fix & & W W A 5 m 5 1 MM? W N W H? K 6 W m M F L m ark/W M m f0 2 5% J6 a. m

United States Patent 3,288,699 APPARATUS FOR *LECTROCHEMECAL SHAPING Kempes F, Trager, Detroit, and Jack A. Cross, Harper Woods, Mich, assignors to Ex-Cell-D Corporation, Detroit, Mich.

Filed Feb. 12, 1964, Ser. No. 344,374 3 Claims. (Cl. 204-224) This invention relates to electrochemical shaping and machining, and more particularly to a method and apparatus for electrochemically or electrolytically removing material from selected portions of a workpiece so as to obtain finished articles of intricate contour such as, for example, gears, gear racks, 'broaches, turbine wheels with integral airfoil blades, bucket or vane rings, splined shafts or rings, and the like.

It has been known for some time that if an electrode connected to the negative terminal of a direct current source of electricity is placed in close proximity to a current conducting workpiece connected to the positive terminal of the source, while a current conductive electrolyte is caused to rapidly flow in the space between the electrode and the workpiece, material is eelctrochemically removed from the surface of the anodic workpiece confronted by the cathodic electrode. By advancing the electrode and the workpiece toward each other at a velocity corresponding to the rate of molecular removal of material from the workpiece, holes may be drilled, cavities may be sunk and contours may be shaped in the workpiece. The process is often called electroplating in reverse because the electrochemical principles involved therein are the same principles permitting ionic transfer of metal or metall-oid elements from an anode to a cathode in an electroplating cell, the only difference being that in electro chemical shaping or machining, the metal or metalloid ions are prevented from plating upon the cathode by the rapidly moving electrolyte or by using an electrolyte composition which does not permit the metal or metalloid ions to remain in solution in the electrolyte.

Electrochemical machining has many applications where conventional machining would fail, would be difficult, or would provide unsatisfactory results because of the hardness or low machineability of the workpiece material, or where conventional machining would impose undue stresses or modfy the physical properties of the workpiece material or of the machined surfaces. Electrochemical machining often presents also many advantages over conventional machining in some applications, even though conventional machining is quite practical and commonly used, because electrochemical machining results in no tool wear, in simplified operations and in improved repeatability, accuracy, surface finish and affords considerable time saving over conventional machining. Also, electrochemical machining leads naturally to automated operations under the control of relatively unskilled workers.

The present invention relates to a method for electrochemically machining intricate workpieces made of electrically conductive material impossible or very difficult to machine by conventional means. Furthermore, even if the workpiece material was such as to be easily machineable by conventional means, electrochemical machining often results in considerable reduction of production costs and time over conventional methods. For example, a turbine wheel with sixty or more integral blades would require upward of twenty-four man-hours to be manufactured by conventional methods. The same turbine wheel manufactured by the method of the invention can be produced in twelve minutes.

The principal object of the invention, therefore, is to provide a method for electrochemically machining intri- "ice cate workpieces at a considerable saving in time and cost as compared to old conventional methods of producing the same part.

Another object of the invention is to electrochemically machine intricate workpieces made of a material which could not be machined by conventional means such as milling, filing, grinding, etc., or made of a, material very difiicult to machine by such conventional means.

A further object of the invention is to electrochemically machine intricate parts without imposing undue mechanical or thermal stress upon the parts, in a manner that leads to high-productivity automatic or automated operations under the control of substantially unskilled labor, with high accuracy and extreme repeatability.

Another object of the invention is to provide a method of electrochemically machining intricate parts with a minimum of operations and setups.

Other objects and advantages will become apparent to those skilled in the art when the following description of an example according to the principles of the invention is considered with the appended drawings in which:

FIGv l is a perspective view of an assembly for the purpose of practicing the electrochemical shaping method of the invention, with portions broken away for the sake of clarity;

FIG. 2 is a view of a portion of the assembly of FIG. I, seen from line 2-2 of FIG. 1;

FIGS. 3a to 3c are schematic representations of the relative positions of typical portions of the tool and workpiece during a machining cycle by means of the assembly of FIG. 1;

FIG. 4 is a perspective view of an assembly for the purpose of practicing a subsequent step in the electrochemical shaping method of the invention;

FIG. 5 is a view of a portion of the assembly of FIG. 4, seen from line 5-5 of FIG. 4;

FIG. 6 is a perspective representation of the relative positions of the tool and workpiece during a machining cycle by means of the assembly of FIG. 4;

FIG. 7 is a perspective schematic representation of an alternate tool configuration; and

FIG. 8 is a sectional view through portions of a workpiece and of the tool according to FIG. 7, to illustrate the principle of operation of the tool of FIG. 7.

The invention will now be described in detail in conjunction with an example of application, such as shaping turbine blades or vanes integral with a turbine wheel. However, it will be clear that, as previously stated, the process is also applicable to manufacturing other intricate parts such as buckets made integral with a ring, compressor rotors or stators, external or internal gears, and the like.

Briefly stated, electro-mechanical shaping according to the principle of the invention is preferably effected in two steps: a roughing-out step and a finishing step, requiring a rough machining setup and a finish machining setup. The finishing step may be performed in turn in two steps or it may be a one-step operation according to the type of tooling used in the finishing operation, as will hereinafter be explained in further details.

Referring now to the drawings and more particularly to FIGS. 1 and 2 which schematically represent an example of a setup assembly for practicing the rough machining step according to the invention, a disc-shaped electrically conductive turbine Wheel blank 10 integral with an axial shaft 11 is held in a holding fixture 12 comprising a stationary member 14 adapted to be mounted on the work holding table (not shown) of an electrochemical machine by means such as clamps coacting with flange 16. Axially aligned within bore 18 of the stationary member 14 and journalled therein, there is a rotatable member 20 provided with .a shoulder portion 22 adapted to bear against the end surface 24 of the stationary member 14, a thrust washer or bearing 26 being interposed between the shoulder portion 22 and the end surface 24. The shaft 11 of the turbine wheel blank, introduced within an axially disposed bore 28 in the rotatable member 20, is securedly clamped in position by way of clamping means such as bolt 30. It is evident that any other convenient means of holding and clamping a workpiece blank upon the rotatable member 20 of the holding fixture 12 may be used, according to the configuration, dimension and shape of the workpiece.

Positioned directly above, as seen in the drawing, and coaxial with the workpiece, there is a roughing electrode tool 32 which is mounted upon a tool holder platen 34 which, in turn, is attached to the end of the linearly movable ram portion 36 of the electrochemical machine (not shown).

The roughing electrode tool 32 consists of an electrically conductive cylindrical enclosure 38 having, on its end confronting the workpiece, an electrically conductive annular flange member 40. The inner diameter surface of the annular flange member 40 is provided with a plurality of segments or teeth 42 for the purpose of machining corresponding slots on the peripheral surface of the workpiece as will be hereinafter explained.

An electric conductor 44 is attached to the electrode tool 32 and another electric conductor 46 is similarly attached to the rotatable shoulder portion 22 of the holding fixture 12. A direct current source, not shown, has its negative terminal connectable via conductor 44 to the electrode tool 32 and its positive terminal connected via conductor 46 to the rotatable shoulder portion 22 of the holding fixture for the purpose of rendering the workpiece, in electrical contact with the rotatable shoulder portion, anodic in relation to the electrode tool.

Electrolyte such as sodium chloride in solution in water at a concentration of grams to 200 grams per liter, is normally supplied to the interface or gap between the electrode tool and the workpiece by being pumped under pressure to the interior of the cylindrical enclosure 38 of the electrode tool 32 by means of at least one flexible tubing 48 connected to a fitting 50 in the cylindrical enclosure, and by flowing substantially radially along the upper face of the workpiece blank 10. The machine table is provided with an enclosure, not shown, preventing excess splashing of the electrolyte, and appropriate outlets and plumbing are provided for returning the electrolyte to the electrolyte circulation and filtration system, not shown.

Projecting from the electrode tool 32 and fastened thereupon, a bracket member 52 carries a pin 54 adapted to engage a cam slot 56 disposed in a block 58 fastened to the rotatable portion 22 of the holding fixture 12. The cam slot 56 has a predetermined contour which will cause the rotatable portion 22 of the workpiece holding fixture to rotate at a predetermined rate when the electrode tool 32 is vertically displaced, as shown in the drawing, in relation to the workpiece, the pin 54 being engaged into the cam slot 56, thereby causing the block 58 and the rotatable portion 22 of the workpiece holder to rotate according to the slope of the cam slot. The bracket 52 is electrically insulated from the electrode tool 32, or the block 58 is insulated from the rotatable portion 20 of the workpiece holding fixture 12, in order I to prevent short circuiting the electrode tool and the workpiece.

In order to effectuate a rough machining operation by means of the setup illustrated in FIGS. 12, the electrode tool is brought toward the workpiece 16 until the annular flange member 40 is in close proximity to the upper faw of the periphery of the workpiece 10, the pin 54 just entering the cam slot 56 in the block 58. Electrolyte flow is started and the power supply, not shown, is connected to the electrode tool and to the workpiece by means of the electrical cables 44 and 46.

As best shown schematically in FIGS. 3a-3c, with an electric current .of several hundred or'thousand amperes, at a voltage preferably of 5 :to 20 v., flowing through the gap 41 between the active faces 43 of the segments or teeth 42 and the receding surfaces of the workpiece confronting such active faces, the electrode tool is fed into the workpiece so as to cause the teeth active faces 43 of the tool annular flange member 50 to selectively erode material from the peripheral edge of the workpiece 10, resulting in a plurality of slots 60 being developed on the periphery of the workpiece 10, the electrolyte flowing, in the direction of the arrows, at high velocity and at substantially high pressure in the gap 41 which may be as narrow as a fraction of a thousandth of an inch or as wide as a few thousandths. Because, when the segments or teeth 42 of the electrode tool are linearly fed in the periphery of the workpiece 10, the workpiece is caused to rotate according to the predetermined slope of the cam slot 56, the resulting slots 60, electrolytically eroded in the peripheral edge of the workpiece, are not in a straight line but are on a curved path. FIGS. 30, 3b and 3c schematically represent, respectively, the relative positons of the segments or teeth 42 of the electrode tool being fed into the periphery of the workpiece 10 at the beginning of the machining operation (FIG. 3a), at some intermediary stage :during the machining operation (FIG. 3b), and at the end of the machining operation (FIG. 30). Rough blade portions 6 2 are left intact between consecutive slots 60.

To prevent excessive uncontrolled erosion of the workpiece, an insulating material may be used to coat the tips of the electrode tool segments or teeth 42 and the surfaces 45 situated between consecutive segments or teeth.

The roughed-out workpiece 10, now provided on its periphery with roughed-out blade blanks 62, is placed in a second holding fixture 64 (FIG. 4) which is similar to the holding fixture 12 of FIG. 1. The workpiece 10 is fastened to the rotatable portion 66 of the holding fixture by way of clamping means such as, for example, a bolt or screw 68. In the tool holder platen 34 of the electrochemical machine is mounted a finishing electrode tool 70 consisting of a cylindrical hollow enclosure or manifold 72 having an end plate 73 provided with a plurality of electrode segments 74 integral with said end plate or fastened thereto.

A bracket 76, provided with a pin 78, is fastened on the electrode tool 72, and the pin 78 is adapted to engage the cam slot 80 in a block 82 fastened to the rotatable portion 66 of the workpiece holding fixture 64.

The holding fixture 64 is provided with an electric cable 46, and the electrode tool 70 is provided with an electric cable 44 and with at least one pipe 48 to introduce electrolyte to the inside :of the manifold 72. The end plate 73 of the electrode tool is provided with electrolyte outlets 84 to distribute electrolyte in the appropriate interfaces between workpiece blade blanks 62 and the electrode segments 74 during the machining operation.

Preparatorily to the finish machining operation, the electrode tool 70 is advanced toward the workpiece 10 until the electrode segments 74 are introduced in the slots 60 between consecutive blade blank-s 62, as shown in FIG. 6. The pin 78 on the end of the bracket 76 engaging the curved vertical portion 85 of the cam slot 80, the workpiece is caused to simultaneously rotate at the appropriate rate .and in the appropriate direction so as to permit the introduction of the electrode segments 74 between consecutive blade blanks 62. The electrolyte flow is started, the electrolyte being caused to flow at high velocity and under pressure from outlets 84 through the interface between surface 92 of the blade blanks 62 and the active face of each electrode segment 74, electric cables 44 and 46 are connected to the appropriate terminals of the power supply, and the rotatable portion 66 of the workpiece holding fixture 64 is rotated by any obvious means such as levers, cams, gears, hydraulic cylinders, etc., with the pin 78 engaging the bottom straight portion 86 of the cam slot 80 until the pin 78 abuts against the side 88 of the horizontal slot 86 (FIG. 5). The active face 90 of each electrode segment 74 is thus caused to erode material from the corresponding surface 92 of each blade blank 62 (FIG. 6). The other faces 94 and 96 of the electrode segments are coated with an insulating material to prevent electrolytic machining dissolution of material from the workpiece surface proximate thereto.

The other surfaces 98 of the blade blanks 62 are finish-machined by means of an electrode tool similar to electrode tool 70 but provided with electrode segments arranged to machine the surfaces 98 of the blade blanks, the pin 78, by engaging the end 100 of the straight portion 86 of the cam slot 80, limiting the amount of rotation of the workpiece in relation to the electrode tool.

In order to simultaneously finish-machine both surfaces 92 and 98 of the blade blanks 62, a finishing tool having a plurality of electrode segment pair 106-108; as illustrated in FIGS. 7-8, may be used. Such a finishing tool comprises a manifold 72 on the bottom end of which are mounted two metal discs 102 and 104 capa-ble of limited rotation one in relation to the other. A plurality of first electrode segments 106 are integral with or fastened to the first disc 102 projecting through apertures 110 in the second disc. A plurality of second electrode segments 108 are integral with or attached to the second disc 104. Electrolyte outlets 112 allow electrolyte to flow from the interior of the manifold 72 along the faces 114 and 116 of the machining electrode seg ments 106 and 108, respectively.

The electrode tool is disposed in relation to the workpiece in such a manner that the pairs of electrode segments 106-108 are placed within the slots 60 between consecutive blade blanks 62, as shown in FIG. 8. Electrolyte flow is started, the workpiece and the electrode tool are connected to the appropriate terminals of the power supply, and discs 102 and 104 are rotated in opposite directions in relation to each other in such a way as to cause the active faces 114 and 116 of the electrode segments 106 and 108 to machine surfaces 98 and 92 respectively of the blade blanks 62, the workpiece being preferably held stationary. Appropriate abutments are provided for limiting the amount of relative rotation of discs 102 and 104, and such rotation may be imparted by any means obvious to those skilled in the art such as levers, cams, gears, hydraulic cylinders, electric motors and the like.

Although there has been disclosed and illustrated a pin-cam arrangement for causing the workpiece to rotate while the machining electrode tool is linearly displaced in relation to said workpiece during the roughing operation (FIGS. 1-3c) and while a similarly disposed pincam arrangement has been disclosed and illustrated in relation to the finish operation for the purpose of facilitating the introduction of the finishing tool electrode segments between the integral blade blanks, combined with abutments for limiting the rotation of the workpiece in relation to the electrode tool during the finish cut (FIGS. 46), it would be obvious to those skilled in the art that many other means may be employed to provide interrelation between the linear motion of the electrode tool and the rotating motion of the workpiece. More particularly, the diverse motions may be effected by servo systems under automatic controls such as may be provided by a programable apparatus built in the electrochemical machining apparatus or by a continuous path tape control. 3

It will be evident to those skilled in the art that the workpiece may be maintained stationary and the electrode tool rotated, without departing from the spirit and scope of the present invention, and that linear motions of both the tool and the workpiece may be combined so as to shape inclined teeth in a rectilinear workpiece such as a gear rack or a breach.

It will also be evident to those skilled in the art of electro-erosion machining by means of electrical discharges through a dielectric fluid flowing between an electrode tool and a workpiece, sometimes called spark machining, that the processes, arrangements and tools of the present invention may be used in such electrical discharge machining.

Having thus described the invention, what is considered novel and sought to be protected by United States Letters Patent is:

1. Apparatus for the electro-erosion of material from an electrically conductive cylindrical workpiece blank having a plurality of outwardly radially extending sections so as to obtain a plurality of substantially identically contoured sections integral with the cylindrical wall of said blank, said apparatus comprising: an electrically conductive electrode tool provided with a base, a plurality of circumferentially spaced integral segments having working surfaces and projecting from said base in the general configuration of a cylinder, said plurality of segments comprising at least one array of segments having their working surfaces facing in one direction of rotation; means for holding said electrically conductive electrode tool in close proximity to the workpiece blank in such a manner that said integral segments intersect spaces between said sections; means connecting said electrode tool in an electric circuit so as to render said tool predominantly cathodic; means connecting said blank in said electric circuit so as to render said' blank anodic; means for introducing a conductive electrolyte at substantially high velocity and high pressure between said working surfaces of said segments and said blank; means for moving said tool and said blank axially in relation to each other; and separate means for simultaneously impressing relative rotational movement upon said tool and said blank, to cause the segments of said tool to electrolytically erode portions of said blank whereby contoured sections are left attached to said blank.

2. The apparatus of claim 1 wherein the said plurality of segments include a second array of independently movable segments interposed between said first array of segments and having working surfaces facing in a direction of rotation opposite from said one direction of rotation.

3. The apparatus of claim 1 wherein at least one surface of each of said segments other than said working surface is electrically insulating.

References Cited by the Examiner UNITED STATES PATENTS 2,282,193 5/1942 Lambrix -10 2,654,821 10/1953 Gillett 219-69 2,674,924 4/ 1954 Nielsen 90-10 2,902,584 9/1959 Ullmann 219-69 2,938,104 5/1960 Paillarse 219-69 3,051,638 8/1962 Clifford et al 204-143 JOHN H. MACK, Primary Examiner.

R, K. Assistqnt Examiner, 

1. APPARATUS FOR THE ELECTRO-EROSION OF MATERIAL FROM AN ELECTRICALLY CONDUCTIVE CYLINDRICAL WORKPIECE BLANK HAVING A PLURALITY OF OUTWARDLY RADIALLY EXTENDING SECTIONS SO AS TO OBTAIN A PLURALITY OF SUBSTANTIALLY IDENTICALLY CONTOURED SECTIONS INTEGRAL WITH THE CYLINDRICAL WALL OF SAID BLANK, SAID APPARATUS COMPRISING: AN ELECTRICALLY CONDUCTIVE ELECTRODE TOOL PROVIDED WITH A BASE, A PLURALITY OF CIRCUMFERENTIALLY SPACED INTEGRAL SEGMENTS HAVING WORKING SURFACES AND PROJECTING FROM SAID BASE IN THE GENERAL CONFIGURATION OF A CYLINDER, SAID PLURALITY OF SEGMENTS COMPRISING AT LEAST ONE ARRAY OF SEGMENTS HAVING THEIR WORKING SURFACES FACING IN ONE DIRECTION OF ROTATION; MEANS FOR HOLDING SURFACES FACING IN ONE DIRECTION OF ROTATION; MEANS CLOSE PROXIMITY TO THE WORKPIECE BLANK IN SUCH A MANNER THAT SAID INTEGRAL SEGMENTS INTERSECT SPACES BETWEEN SAID SECTIONS; MEANS CONNECTING SAID ELECTRODE TOOL IN AN ELECTRIC CIRCUIT SO AS TO RENDER SAID TOOL PREDOMINANTLY CATHODIC; MEANS CONNECTING SAID BLANK IN SAID ELECTRIC CIRCUIT SO AS TO RENDER SAID BLANK ANODIC; MEANS FOR INTRODUCING A CONDUCTIVE ELECTROLYTE AT SUBSTANTIALLY HIGH VELOCITY AND HIGH PRESSURE BETWEEN SAID WORKING SURFACES OF SAID SEGMENTS AND SAID BLANK; MEANS FOR MOVING SAID TOOL AND SAID BLANK AXIALLY IN RELATION TO EACH OTHER; AND SEPARATE MEANS FOR SIMULTANEOUSLY IMPRESSING RELATIVE ROTATIONAL MOVEMENT UPON SAID TOOL AND SAID BLANK, TO CAUSE THE SEGMENTS OF SAID TOOL TO ELECTROLYTICALLY ERODE PORTIONS OF SAID BLANK WHEREBY CONTOURED SECTIONS ARE LEFT ATTACHED TO SAID BLANK. 